Many types of crash sensors have been proposed to be used with passenger restraint systems in automobiles, airplanes and other vehicles. Such passenger restraint systems include automatically retracting seat belts and inflatable air bags. Most crash sensors function to effect the closure of an electrical switch upon sensing a crash of a predetermined severity. When used with inflatable air bags, for example, this switch closure completes a circuit to provide energy to a pyrotechnic element which in some cases opens a bottle of compressed gas or in other cases ignites a pyrotechnic gas generator.
When the sensor is not located forward in the crush zone of a vehicle the energy levels are smaller by a factor of at least 10, so it must be responsive to very low energies.
To date damped mechanical sensors have only been used for sensing automobile crashes in the crush zone or as very sensitive arming or safing sensors on the firewall. There are advantages of using damped sensors outside of the crush zone and in particular in the passenger compartment. These advantages include a substantial system cost reduction and increase in system reliability. In the case of forward sensors, triggering is preferably caused by a velocity change which is relatively independent of the duration of the impact, whereas for non-crush zone sensors, the velocity change required to trigger the sensor varies significantly as a function of pulse duration. Finally, all mechanical non-crush zone sensors require release mechanisms actuated by very little energy. The difficulty of satisfying these requirements has contributed to the fact that a damped sensor located outside of the crush zone of the car has heretofore not been used to actuate a mass produced air bag restraint system.
The ability to locate crash sensors outside the frontal crush zone, and, preferably, in the passenger compartment, which can rapidly discriminate between crashes that do and do not require air bag deployment results in a substantially simpler air bag system.